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BC(1) FreeBSD General Commands Manual BC(1)
NAMEbc -- arbitrary-precision arithmetic language and calculator
SYNOPSISbc [-chlv] [-eexpression] [file...]
DESCRIPTIONbc is an interactive processor for a language which resembles C but pro-
vides unlimited precision arithmetic. It takes input from any expres-
sions on the command line and any files given, then reads the standard
input.
Options available:
-cbc is actually a preprocessor for dc(1), which it invokes auto-
matically, unless the -c (compile only) option is present. In
this case the generated dc(1) instructions are sent to the stan-
dard output, instead of being interpreted by a running dc(1)
process.
-eexpression, --expressionexpression
Evaluate expression. If multiple -e options are specified, they
are processed in the order given, separated by newlines.
-h, --help
Prints usage information.
-l, --mathlib
Allow specification of an arbitrary precision math library. The
definitions in the library are available to command line expres-
sions.
-v, --version
Prints version information.
The syntax for bc programs is as follows: `L' means letter a-z; `E' means
expression; `S' means statement. As a non-portable extension, it is pos-
sible to use long names in addition to single letter names. A long name
is a sequence starting with a lowercase letter followed by any number of
lowercase letters and digits. The underscore character (`_') counts as a
letter.
Comments
are enclosed in /* and */
are enclosed in # and the next newline
The newline is not part of the line comment, which in itself is a non-
portable extension.
Names
simple variables: L
array elements: L [ E ]
The words `ibase', `obase', and `scale'
The word `last' or a single dot
Other operands
arbitrarily long numbers with optional sign and decimal point
( E )
sqrt ( E )
length ( E ) number of significant decimal digits
scale ( E ) number of digits right of decimal point
L ( E , ... , E )
The sequence `\<newline><whitespace>' is ignored within numbers.
Operators
The following arithmetic and logical operators can be used. The seman-
tics of the operators is the same as in the C language. They are listed
in order of decreasing precedence. Operators in the same group have the
same precedence.
OperatorAssociativityDescription
++ -- none increment, decrement
- none unary minus
^ right power
* / % left multiply, divide, modulus
+ - left plus, minus
= += -= *= /= %= ^= right assignment
== <= >= != < > none relational
! none boolean not
&& left boolean and
|| left boolean or
Note the following:
+o The relational operators may appear in any expression. The
IEEE Std 1003.1-2008 (``POSIX.1'') standard only allows them in
the conditional expression of an `if', `while' or `for' state-
ment.
+o The relational operators have a lower precedence than the
assignment operators. This has the consequence that the
expression a=b < c is interpreted as (a=b) < c, which is
probably not what the programmer intended.
+o In contrast with the C language, the relational operators all
have the same precedence, and are non-associative. The expres-
sion a < b < c will produce a syntax error.
+o The boolean operators (!, && and ||) are non-portable exten-
sions.
+o The boolean not (!) operator has much lower precedence than the
same operator in the C language. This has the consequence that
the expression !a < b is interpreted as !(a < b). Prudent pro-
grammers use parentheses when writing expressions involving
boolean operators.
Statements
E
{ S ; ... ; S }
if ( E ) S
if ( E ) S else S
while ( E ) S
for ( E ; E ; E ) S
null statement
break
continue
quit
a string of characters, enclosed in double quotes
print E ,..., E
A string may contain any character, except double quote. The if state-
ment with an else branch is a non-portable extension. All three E's in a
for statement may be empty. This is a non-portable extension. The con-
tinue and print statements are also non-portable extensions.
The print statement takes a list of comma-separated expressions. Each
expression in the list is evaluated and the computed value is printed and
assigned to the variable `last'. No trailing newline is printed. The
expression may also be a string enclosed in double quotes. Within these
strings the following escape sequences may be used: `\a' for bell
(alert), `\b' for backspace, `\f' for formfeed, `\n' for newline, `\r'
for carriage return, `\t' for tab, `\q' for double quote and `\\' for
backslash. Any other character following a backslash will be ignored.
Strings will not be assigned to `last'.
Function definitions
define L ( L ,..., L ) {
auto L, ... , L
S; ... S
return ( E )
}
As a non-portable extension, the opening brace of the define statement
may appear on the next line. The return statement may also appear in the
following forms:
return
return ()
return E
The first two are equivalent to the statement ``return 0''. The last
form is a non-portable extension. Not specifying a return statement is
equivalent to writing ``return (0)''.
Functions available in the math library, which is loaded by specifying
the -l flag on the command line
s(x) sine
c(x) cosine
e(x) exponential
l(x) log
a(x) arctangent
j(n,x) Bessel function
All function arguments are passed by value.
The value of a statement that is an expression is printed unless the main
operator is an assignment. The value printed is assigned to the special
variable `last'. This is a non-portable extension. A single dot may be
used as a synonym for `last'. Either semicolons or newlines may separate
statements. Assignment to scale influences the number of digits to be
retained on arithmetic operations in the manner of dc(1). Assignments to
ibase or obase set the input and output number radix respectively.
The same letter may be used as an array, a function, and a simple vari-
able simultaneously. All variables are global to the program. `Auto'
variables are pushed down during function calls. When using arrays as
function arguments or defining them as automatic variables, empty square
brackets must follow the array name.
For example
scale = 20
define e(x){
auto a, b, c, i, s
a = 1
b = 1
s = 1
for(i=1; 1==1; i++){
a = a*x
b = b*i
c = a/b
if(c == 0) return(s)
s = s+c
}
}
defines a function to compute an approximate value of the exponential
function and
for(i=1; i<=10; i++) e(i)
prints approximate values of the exponential function of the first ten
integers.
$ bc -l -e 'scale = 500; 2 * a(2^10000)' -e quit
prints an approximation of pi.
COMMAND LINE EDITINGbc supports interactive command line editing, via the editline(3)
library. It is enabled by default if input is from a tty. Previous
lines can be recalled and edited with the arrow keys, and other GNU
Emacs-style editing keys may be used as well.
The editline(3) library is configured with a .editrc file - refer to
editrc(5) for more information.
FILES
/usr/share/misc/bc.library math library, read when the -l option is
specified on the command line.
COMPATIBILITY
The -q and --quiet options are no-ops for compatibility with some other
implementations of bc and their use is discouraged.
SEE ALSOdc(1)STANDARDS
The bc utility is compliant with the IEEE Std 1003.1-2008 (``POSIX.1'')
specification.
The flags [-ce], as well as the parts noted above, are extensions to that
specification.
HISTORY
The bc command first appeared in Version 6 AT&T UNIX. A complete rewrite
of the bc command first appeared in OpenBSD 3.5.
AUTHORS
The original version of the bc command was written by Robert Morris and
Lorinda Cherry. The current version of the bc utility was written by
Otto Moerbeek.
BUGS
The `quit' statement is interpreted when read, not when executed.
Some non-portable extensions, as found in the GNU version of the bc util-
ity are not implemented (yet).
FreeBSD 11.1 November 21, 2015 FreeBSD 11.1